A conventional ultrasonic diagnostic apparatus is disclosed in Japanese Unexamined Patent Application Publication No. 11-113913, for example, in which a body cavity radial scan type ultrasonic probe (including an ultrasonic endoscope having an optical observation window) having an ultrasonic transducer and a position detector at the distal end of a long and narrow insert portion to be inserted to a body cavity is inserted or withdrawn through a curved or bent lumen. Thus, plural ultrasonic tomographic images are obtained, and ultrasonic image data of a space along a lumen path thereof is obtained. Also, a body cavity convex scanning type ultrasonic probe having an ultrasonic transducer and a position detector at the distal end of an insert portion thereof is known in which the ultrasonic probe is inserted into a lumen and is rotated about an insert axis. Thus, plural ultrasonic tomographic images are obtained, and ultrasonic image data of the lumen space is obtained.
Furthermore, another ultrasonic diagnostic apparatus is known in which an ultrasonic probe for external use provided with a position detector irradiates ultrasonic wave to a body to be examined from outside of the body and is moved or rotated at the same time. Thus, plural ultrasonic tomographic images are obtained, and ultrasonic image data of the space is obtained. The ultrasonic diagnostic apparatus is proposed in Japanese Unexamined Patent Application Publication No. 10-216127 and Registered Utility Model No. 3040306.
Various methods for expressing an ultrasonic image on a monitor screen based on ultrasonic image data obtained in these ultrasonic diagnostic apparatus are examined. Following first and second expressing methods are adopted in the first patent document and a following third expressing method is adopted in the second patent document and third patent document.
In the first expressing method, three-dimensional image data expressed by orthogonal coordinates is created by averaging parts in which plural ultrasonic tomographic images overlap and/or by interpolating between ultrasonic tomographic images. Then, based on the three-dimensional image data, a cross-sectional image cut at a plane is expressed.
In the second expressing method, three-dimensional image data expressed by orthogonal coordinates is created by averaging parts in which plural ultrasonic tomographic images overlap and/or by interpolating between ultrasonic tomographic images. Then, based on the three-dimensional image data, an ultrasonic three-dimensional image is expressed.
In the third expressing method, a change in coordinate positions of an ultrasonic probe is obtained from an output of a position detector. Plural two-dimensional ultrasonic tomographic images are moved by an amount corresponding to a change in position of scan planes and are stacked. Thus, a pseudo three-dimensional image is expressed.
In an application of this kind of ultrasonic diagnostic apparatus, an operator may diagnose by moving an ultrasonic probe within an organ of a lumen form such as the stomach, the esophagus and the bowels. In this case, performing three observations, which will be described below, is important for estimating the prognosis and for determining an operation/treatment range.
A first observation is performed for finding from where to where a lesion spreads and invades along a lumen.
A second observation is performed for finding how deep the lesion invades in a direction vertical to a surface of the lumen.
A third Observation is performed for finding how wide and how deep the lesion invades to an organ or a portal blood vessel and so on which are in a deeper part over the lumen such as the pancreas or the like.
In order to perform the first to third observations, the first to third expressing methods are used.
On the other hand, a so-called external ultrasonic diagnostic apparatus has been conventionally proposed for creating a tomographic image by transmitting and receiving ultrasonic wave from an ultrasonic probe to and from the outside of a body to be examined. For example, one disclosed in Japanese Unexamined Patent Application Publication No. 9-192128, Japanese Unexamined Patent Application Publication No. 11-47133 or Japanese Unexamined Patent Application Publication No. 2001-17433 detects a positional relationship between an observing portion and an ultrasonic probe and/or a scan plane thereof (therefore, a position and direction of an ultrasonic tomographic image) by means of a position and direction detecting portion of using a magnetic field and displays the positional relationship on a monitor. When this kind of ultrasonic diagnostic apparatus displays a tomographic image on a monitor, a picture expressing an ultrasonic probe called probe mark is superimposed over a human-shape image called body mark expressing a body to be examined, which is prepared by the apparatus in advance. With the construction and the operation, an operator can easily recognize how and which part of a body to be examined is observed to obtain a given tomographic image during a diagnosis using images during and after an examination.
In this kind of conventional internal ultrasonic diagnostic apparatus, an operator generally uses an ultrasonic endoscope having an ultrasonic transducer as an ultrasonic probe and a CCD camera at the distal end of the ultrasonic endoscope. Then, the operator inserts the distal end of the ultrasonic endoscope into the vicinity of an area of concern such as a tumor by observing an optical image from the CCD camera at the same time. Next, in accordance with a position of the organ appearing on an ultrasonic image, and based on anatomical knowledge of the operator, the operator determines the position and direction of the ultrasonic image obtained by the ultrasonic transducer. Next, the operator projects the area of concern in the ultrasonic image by moving the distal end of the ultrasonic endoscope.